. and cities across this country, already on alert. >> today, security is stepped up around new york and washington, d.c., because of the threat involving a car bomb aimed at bridges and tunnels. >> with more on the possible plot, we go to abc's scott goldberg, in washington. good morning to you, scott. >> reporter: good morning, rob and tanya. u.s. officials have been bracing for this type of plot, ever since they saw documents mentioning a september 11th anniversary attack in osama bin laden's hideout. they are now sorting through information the cia came across less than two days ago. in the hearts of new york city, where police already were on alert, now, they're adding extra hours to their shifts. also in the nation's capital, they're taking extra precautions because of a terror threat tied to the 9/11 anniversary. >> it's accurate that there's specific, creditable, but unconfirmed threat information. >> reporter: u.s. officials say they discovered a plot concocted by al qaeda's new leader, ayman al zawahiri, who has vowed to avenge the death of his predecessor, osama bin laden.